power: pmic: add Ricoh RN5T567 PMIC support

Add device model enabled PMIC driver for Ricoh RN5T567 PMIC used
on Colibri iMX7.

Signed-off-by: Stefan Agner <stefan.agner@toradex.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

doc/device-tree-bindings/pmic/rn5t567.txt

@@ -0,0 +1,17 @@
+Ricoh RN5T567 PMIC
+
+This file describes the binding info for the PMIC driver.
+
+Required properties:
+- compatible: "ricoh,rn5t567"
+- reg: depending on strapping, e.g. 0x33
+
+With those two properties, the PMIC device can be used to read/write
+registers.
+
+Example:
+
+rn5t567@33 {
+	compatible = "ricoh,rn5t567";
+	reg = <0x33>;
+};